Method for calibrating an AOA location system for frequency hopping air interfaces

ABSTRACT

A method for calibrating an antenna and signal processing system enabling angle or arrival (AOA) determination for a frequency hopping signal, in which a calibration coefficient is determined in response to one or more calibration signals injected into the system at one or more of the frequencies in the hopping sequence and proximate in time to reception of the communication signal. The calibration coefficients are reflective of a frequency and time dependent parameter of a path between the antenna and wireless location sensor. The AOA is determined as a function of the calibration coefficient and the radio frequency energy of the received communication signal. Several embodiment of the method are illustrated.

CROSS REFERENCES

[0001] The present application is co-pending with and claims prioritybenefit of provisional application entitled “ANGLE OF ARRIVALCALCULATION ON FREQUENCY HOPPING AIR INTERFACES”, U.S. Application Ser.No. 60/443,838 and filed on Jan. 31, 2003, the entirety of which ishereby incorporated herein by reference.

[0002] The present application is also co-pending and concurrently filedwith related applications “A METHOD FOR CALIBRATING AN AOA LOCATIONSYSTEM FOR ALL FREQUENCIES IN A FREQUENCY HOPPING SIGNAL” applicationSer. No. ______ and “A METHOD FOR ANGLE OF ARRIVAL DETERMINATION ONFREQUENCY HOPPING AIR INTERFACES” application Ser. No. ______ and arehereby incorporated herein by reference.

BACKGROUND

[0003] In the United States, mobile wireless appliance locatingequipment is being deployed for the purpose of locating wireless callerswho dial 911. Other services in addition to emergency call servicing arecontemplated and are referred to as location based services (LBS).Wireless location equipment is typical employed as a overlay to wirelesscommunication networks, thus forming a network overlay geo-locationsystem.

[0004] In operation, these network overlay location systems takemeasurements on RF transmissions from mobile appliances at base stationlocations surrounding the mobile appliance, and estimate the location ofthe mobile appliance with respect to the base stations. Because thegeographic location of the base stations is known, the determination ofthe location of the mobile appliance with respect to the base stationpermits the geographic location of the mobile appliance to bedetermined. The RF measurements of the transmitted signal at the basestations can include the time of arrival, the angle of arrival, thesignal power, or the unique/repeatable radio propagation path (radiofingerprinting) derivable features. In addition, the geo-locationsystems can also use collateral information, e.g., information otherthan that derived for the RF measurement to assist in the geo-locationof the mobile appliance, i.e., location of roads, dead-reckoning,topography, map matching etc.

[0005] Angle of arrival (AOA) is a well-known measurement that can bemade on an RF signal for the purpose of locating a mobile applianceoperating in a wireless communications network. There have been manymethods disclosed to produce the AOA. Many of these methods use somemethod of calibration to take into account the dynamic nature of thecomponents in path prior to the signal measurements made to estimateAOA. In general, the calibration is composed of coupling or injecting aknown signal simultaneously into the receive signal paths at or close tothe antenna array, and measuring the inter-channel characteristics ofthe test signal to characterize the traversed components (antenna beamformers, cables, RF distribution units, filters, etc.).

[0006] However these methods do not specifically deal with the problemsthat arise when the mobile appliance is operating in a wireless networkthat utilizes frequency hopping, such as the GSM air interface. The useof frequency hopping in wireless air interfaces is well known, andexemplified by GSM, the most widely deployed air interface in the world,therefore there is a need to address the problems confronted whenlocating frequency hopping mobile appliances.

[0007] The current subject matter provides novel approaches forefficiently calibrating an antenna and signal processing equipment, toallow generating accurate AOA measurements in equipment intended tolocate wireless mobile appliances operating in a network employingfrequency hopping. The novel approaches includes calibrationmethodologies and configurations.

[0008] In order to obviate the deficiencies of the prior art, it is anobject of the current subject matter to present, in a network overlaygeolocation system, a novel improvement in a method for locating amobile appliance. The method including determining the AOA of an uplinksignal from the mobile appliance at a base station from measurements, bya wireless location sensor, of an attribute of the uplink signal and afrequency specific calibration of a path between a multi element antennaarray and the wireless location sensor. The novel improvement, whereinthe uplink signal is a frequency hopping signal and including collectingsegments of a frequency hopping signal associated with each hop andcalibrating the path, at approximately the respective segment's hopfrequency and proximate in time to collecting the respective segments.The improvement also including, estimating the AOA of a frequencyhopping signal from the collected segments and the path calibrations.

[0009] It is also an object of the present subject matter to present, ina network overlay geolocation system, an improvement to a method forlocating a mobile appliance. The method including determining the AOA ofan uplink signal from the mobile appliance at a base station frommeasurements, by a wireless location sensor, of an attribute of theuplink signal and a frequency specific calibration of a path between amulti element antenna array and the wireless location sensor. The novelimprovement, wherein the uplink signal is a frequency hopping signal andfurther includes collecting segments of a frequency hopping signalassociated with a specific hop; calibrating the path, at approximatelythe specific hop's frequency, proximate in time to the collecting ofeach segment, over a plurality of hopping sequence cycles. Theimprovement also including estimating the AOA of a frequency hoppingsignal from the collected segments associated with the specific hop andthe path calibrations at approximately the specific hop's frequency.

[0010] It is still a object of the current subject matter to present, ina network overlay geolocation system, an improvement to a method forlocating a mobile appliance. The method including determining the AOA ofan uplink signal from the mobile appliance at a base station frommeasurements, by a wireless location sensor, of an attribute of theuplink signal and a frequency specific calibration of a path between amulti element antenna array and the wireless location sensor. The novelimprovement, wherein the uplink signal is a frequency hopping signal andfurther includes collecting segments of a frequency hopping signalassociated with each frequency hop; calibrating the path, at apredetermined frequency and proximate in time to the collecting of eachof the segments. The improvement also including estimating the AOA of afrequency hopping signal from the collected segments and the pathcalibrations at the predetermined frequency.

[0011] It is an additional object of the current subject matter topresent, in a network overlay geolocation system, a novel improvement toa method for locating a mobile appliance. The method includingdetermining the AOA of an uplink signal from the mobile appliance at abase station from measurements, by a wireless location sensor, of anattribute of the uplink signal and a frequency specific calibration of apath between a multi element antenna array and the wireless locationsensor. The novel improvement, wherein the uplink signal is a frequencyhopping signal and further includes collecting calibration data for eachof the hop frequencies in the frequency hopping sequence; determining arelationship between the calibration data at a selected hop frequencyand the other hop frequencies; collecting segments of a frequencyhopping signal associated with each hop; calibrating the path, at theselected hop frequency and proximate in time to collecting the segmentassociated with each hop. The improvement further including estimatingthe AOA of a frequency hopping signal from the collected segments, thepath calibrations at the selected hop frequency and the determinedrelationship between the calibration data for the selected hop frequencyand the respective hop's frequency.

[0012] It is another object of the present subject matter to disclose anovel method of calibrating an antenna array and signal processing forreceiving a frequency hopping communication signal. The method includingthe steps of obtaining frequency hopping operational information of thesignal, receiving the signal, and injecting calibration signals atfrequencies of the frequency hopping sequence in response to receipt ofthe communication signal. The method further including determiningcalibration coefficients C₁ and C₂ for said at least two frequencies andapplying C₁ and C₂ to calibrate the antenna and signal processingequipment to a received signal.

[0013] It is still another object of the present subject matter todisclose a novel method of calibrating an antenna array and signalprocessing for receiving a frequency hopping communication signal. Themethod including obtaining frequency hopping operation information ofthe signal and receiving the signal. The method injecting a calibrationsignal at one frequency of the frequency hopping sequence of the signalin response to receipt of the signal and determining a calibrationcoefficient C₁ for the one frequency and, applying C₁ to a receivedsignal at each frequency in the received signal to calibrate the antennaand signal processing equipment.

[0014] It is yet another object of the present subject matter todisclose a novel method of determining an angle of arrival of afrequency hopping communication signal. The method including obtainingfrequency hopping operation information of the signal and receiving thesignal over multiple hops of the same frequency. The method includinginjecting a calibration signal at one frequency of the frequency hoppingsequence of the signal in response to receipt of signal and determininga calibration coefficient C₁ for said one frequency. The method furtherincludes determining the AOA of the signal based on the hops of thesignal having said one frequency and the calibration coefficient C₁.

[0015] It is still yet another object of the present subject matter todisclose a novel method of calibrating an antenna array and signalprocessing for receiving a frequency hopping communication signal. Themethod including periodically injecting calibration signals atfrequencies in the frequency band of the system and determining andstoring calibration coefficients for the frequencies. The method thendetermines relationships relating calibration coefficient of onefrequency to the calibration coefficients of each of the otherfrequencies using the stored calibration coefficients. The methodinvolves obtaining the frequency hopping operational information of thesignal and receiving said signal. The method further includes injectinga calibration signal at one frequency in response to receipt of saidsignal and determining a calibration coefficient C₁ for said onefrequency and, determining calibration coefficients for said otherfrequencies based on the calibration coefficient for said one frequencyand the determined relationships. The method includes applying thecalibration coefficients corresponding to the frequencies of thereceived signal to the received signal.

[0016] These objects and other advantages of the disclosed subjectmatter will be readily apparent to one skilled in the art to which thedisclosure pertains from a perusal or the claims, the appended drawings,and the following detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is an illustrative system diagram of a system path withcalibration and location components.

[0018]FIG. 2 is a flow chart of a method according to an embodiment ofthe present subject matter.

[0019]FIG. 3 is a flow chart of a method according another embodiment ofthe present subject matter.

[0020]FIG. 4 is a flow chart of a method according still anotherembodiment of the present subject matter.

[0021]FIG. 5 is a flow chart of a method according to yet anotherembodiment of the present subject matter.

[0022]FIG. 6 is a flow chart of a method according to an additionalembodiment of the present subject matter.

[0023]FIG. 7 is a flow chart of a method according to a furtherembodiment of the present subject matter.

[0024]FIG. 8 is a flow chart of a method according to a still furtherembodiment of the present subject matter.

[0025]FIG. 9 is a flow chart of a method according to yet a furtherembodiment of the present subject matter.

DETAILED DESCRIPTION

[0026] This present subject matter will be described with respect to aGSM network, however the subject matter is applicable and can be appliedto a variety of wireless communication networks, and thus is not limitedto a GSM network. Thus subject matter of the disclosure will be describewith respect to a network overlay geo-location system that deriveslocation from the uplink signal emitted from a mobile appliance, howeverit is applicable and can also be applied in the context of differentlocation methods, and thus is not limited to the network overlaylocation system described. The selection of the specific network andlocation system is for illustrative purposes only.

[0027] The prior art method to determine AOA is to estimate a line ofbearing perpendicular to the face of the antenna array based oncollecting a segment of RF signal at multiple antenna elements in thearray. Either just prior to, or just after the collection of the segmentof RF signal, the calibration signal is injected into the path at ornear the antenna array to calibrate the path between the antenna and thesignal collection hardware. The collected calibration data is generallymade up of a series of complex voltages for each antenna element, andthe relationship between the calibration signal injected into eachantenna path is known. The calibration signal is generally at or nearthe RF frequency of the signal for which an AOA estimate is to be made.FIG. 1 is an illustration of a representative path with multi-elementantenna array 101, a calibration source 102 a for injecting calibrationsignals (or alternatively calibration source 102 b that transmits thecalibration signal to the antenna), signal processing equipment 103 suchas beam formers, amplifiers or other like equipment and the wirelesslocation sensor 104 that determines the angle of arrival.

[0028] The calibration data may include apriori knowledge about theantenna, receiving system and characteristics of the air interface. Thecalibration signal injection must be performed very close in time to thecollection of the signal of interest, and at or very near the same RFfrequency. This is because the characteristics of the path between theantenna and the signal collection functions have dynamic time andfrequency dependent characteristics.

[0029] However, in the case of uplink signals that frequency hop, whichis within the subject matter of the present disclosure, the hopdurations are generally much shorter than the duration of the segment ofRF that must be collected to produce an AOA estimate. Therefore,multiple RF frequencies will be contained in the segment of RF that iscollected to estimate the AOA using the prior art location methods.Moreover, the hopping occurs with little time spent in the transitionfrom one frequency to another. Generally, the transition time isinsufficient to allow the calibration signal to be injected betweenhops. Thus these conditions do not allow the approach of single RFfrequency calibration prior to, or after the signal of interest RFsegment collection to be used.

[0030] The subject matter of this disclosure presents methodologies andconfigurations to provide path calibration for these circumstances.

[0031] In general, the hop RF frequencies, the hopping sequence and timephase, and the hop durations are known apriori. As used in the remainderof the disclosure frequency hopping sequence includes informationregarding one or more of hopping sequence, hopping duration, phase, andother operation parameters of a frequency hopping signal. Severalmethods that can be applied to account for the hopping are describedherein:

[0032] In one aspect of the subject matter, all of the RF frequencies(f₁ . . . f_(N)) that will be used in the hopping sequence can becalibrated just prior to or just after the segment of RF energy,interchangeable referred to as RF energy of the received signal or justthe received signal, is collected for the signal of interest, emergencycall or LBS call. In this aspect each of the frequencies hopped to canbe calibrated with its corresponding calibration data (C₁ . . . C_(N)),where f₁ corresponds to C₁, and f₂ to C₂, etc. In this approach The RFcalibration signal injection hardware used in prior art single frequencycases can be utilized, with the only new requirement on the calibrationequipment would be the need for the calibration source to be able totune rapidly through the hop frequencies of the hopping sequence so thatthe calibration can occur rapidly and close (or proximate in time) tothe collection of the RF energy of the signal of interest.

[0033]FIG. 2 is an simple flow chart of an embodiment of the presentsubject matter utilizing the above approach to calibrate the signal pathfrom the antenna array to the wireless location sensor. In the firststep the frequency hopping sequence of the hopping sequence of thesignal (f₁,f₂ . . . f_(N)) is obtained from the transmitting mobile overa control channel or other network entity of the host network as shownin block 201. The mobile's signal which may or may not includecommunication data is received at the multi-element antenna array asshown in block 203. After receiving the RF energy or received signal,the calibration source injects calibration signals at each frequency ofthe hopping sequence (f₁,f₂ . . . f_(N)) into the path at or near theantennas as shown in block 205. The injection of the calibration signalis triggered by the receipt of the signal of interest. These calibrationsignals are used to determine calibration coefficients (C₁,C₂ . . .C_(N)) for each of the frequencies as illustrated in block 207. With thecalibration coefficients determined and the signal received the path canbe calibrated for each frequency hop of the received signal using thecorresponding calibration coefficients as shown in block 209. Thecalibration coefficients can also be used on a subsequent receivedsignal with the assumption it is received close or proximate to the timethe calibration signal where injected. The calibrated measurements ofthe received signal can know be used to determine the AOA of thetransmitted signal using known methods.

[0034] Similarly FIG. 3 is a flow chart of a method in which theinjection of the calibration signals are not triggered or initiated bythe reception of the signal of interest.

[0035] In the first step the frequency hopping sequence of the hoppingsequence of the signal (f₁,f₂ . . . f_(N)) is obtained from thetransmitting mobile over a control channel or other network entity ofthe host network as shown in block 301. The calibration source injectscalibration signals at each frequency of the hopping sequence (f₁,f₂ . .. f_(N)) into the path at or near the antennas as shown in block 303.The injection of the calibration signal is triggered periodically orupon a measured or anticipated deviation of the accuracy of a systemparameter. These calibration signals are used as above to determinecalibration coefficients (C₁,C₂ . . . C_(N)) for each of the frequenciesas illustrated in block 305. These calibration coefficients are thenstored is a memory device, software or hardware as shown in block 307for latter use when a signal of interest in received. A signal issubsequently received at the multi-element antenna array as shown inblock 309 and the calibration coefficients stored in memory are appliedto the received signal to calibrate the received signal to the path orvice versa as shown in block 311.

[0036] Another aspect of the disclosed subject matter takes the approachthat calibration can be done on a single RF frequency either just prioror just after the signal of interest collection event, and then all RFfrequencies of the hopping sequence can be calibrated with the single RFfrequency. The advantage of this approach is that it is simple and canuse the same calibration equipment as is typically available when singleRF frequency signal are calibrated. The disadvantage of this approach isthat the single calibration frequency most likely will not be completelyaccurate for all of the hopping frequencies, and errors can beintroduced into resultant AOA estimates.

[0037]FIG. 4 is an simple flow chart of an embodiment of the presentsubject matter utilizing the above approach to calibrate the signal pathfrom the antenna array to the wireless location sensor using only onecalibration signal and calibration coefficient. In the first step thefrequency hopping sequence of the hopping sequence of the signal (f₁,f₂. . . f_(N)) is obtained as shown in block 401. The mobile's signal isreceived at the multi-element antenna array as shown in block 403. Afterreceiving the signal which is a triggering event, the calibration sourceinjects a single calibration signal at a frequency f_(k) selected fromthe frequencies of the hopping sequence (f₁,f₂ . . . f_(N)) into thepath as shown in block 405. The selected frequency can be arbitrarilyselected or can be selected as a function of a statistic of all thefrequencies in the hopping sequence, such as an average, mean, mode,first moment or other statistic of the frequencies in the hoppingsequence. This calibration signal is used to determine a calibrationcoefficient C_(k) for the frequency f_(k) as illustrated in block 407.With the calibration coefficient determined and the signal received, thepath is calibrated for each frequency hop of the received signal usingthe calibration coefficient C_(k) for each frequency as shown in block409. As the calibration varies as a function of frequency it ispreferable to select f_(k) such that it is close the average or the meanof the frequencies (f₁,f₂ . . . f_(N)) or it can also be selected as thestarting or first frequency of the hopping sequence for convenience.

[0038] Similarly FIG. 5 is a flow chart of a method in which theinjection of the calibration signal is not triggered or initiated by thereception of the signal of interest. In the first step the frequencyhopping sequence of the hopping sequence of the signal (f₁,f₂ . . .f_(N)) is obtained from the transmitting mobile over a control channelor other network entity of the host network as shown in block 501. Thecalibration source injects a single calibration signal at a frequencyf_(k) selected as described above from the frequencies of the hoppingsequence (f₁,f₂ . . . f_(N)) into the path as shown in block 503. Thecalibration signal is used to determine a calibration coefficient C_(k)for the frequency f_(k) as illustrated in block 505. The injection ofthe calibration signal is triggered periodically or upon a measured oranticipated deviation of the accuracy of a system parameter. Thiscalibration signal is stored as shown in block 507. A signal issubsequently received at the multi-element antenna array as shown inblock 509 and the calibration coefficient stored in memory is used tocalibrate the path for the each of the frequencies of the receivedsignal as shown in block 511.

[0039] Another aspect of the disclosed subject matter illustrates thatdetermining AOA calibration can be done on a single RF frequency eitherjust prior or just after the signal of interest collection event. Thisapproach only collects RF energy from the appliance of interest whenoperating on the frequency used in the AOA calibration. For example, ifthe hopping sequence contains three frequencies f₁,f₂,f₃ and thus thesignal transmitted from the mobile appliance cycles through the sequence(f₁, f₂, f₃,f₁,f₂,f₃,f₁, f₂, f₃ . . . etc.) Therefore if the frequencyselected for the calibration signal is f₂ only the 2^(nd),5^(th),8^(th)11^(th) hops will be collected by the WLS, wherein the other methodsshow collecting each hop of the received signal. This method works wellwhen the total number of RF frequencies in the hopping set is small andvisited in a relatively uniform fashion as demonstrated in the example.However, in the case of some GSM installations, the number of RFfrequencies in the hopping sequence is 5 or 6, so if one frequency isused from the set, the collection time would have to be increased by afactor of 5 or 6, which may be disadvantageous. The calibrationequipment needed to implement this method can be identical to that usedfor the single RF frequency case.

[0040]FIG. 6 is a simple flow chart of an embodiment of the presentsubject matter utilizing the above approach to determine the AOA of afrequency hopping signal from a mobile appliance which includescalibrating the signal path between from the antenna array to thewireless location sensor for the frequency hops having the samefrequency using only one calibration signal and calibration coefficient.In the first step the frequency hopping sequence of the hopping sequenceof the signal (f₁,f₂ . . . f_(N)) is obtained as shown in block 601. Themobile's signal is received at the multi-element antenna array overmultiple hops of frequency f_(k) as shown in block 603. After receivingthe signal which is a triggering event, the calibration source injects asingle calibration signal at a frequency f_(k) selected from thefrequencies of the hopping sequence (f₁,f₂ . . . f_(N)) into the path asshown in block 605. This calibration signal is used to determine acalibration coefficient C_(k) for the frequency f_(k) as illustrated inblock 607. The calibration coefficient C_(k) is used only to calibratesthe frequency hops having the frequency f_(k). The WLS collects energyfrom only those frequency hops with a frequency f_(k) and along with thecalibration coefficient C_(k) are used to determine the AOA of thereceived signal as shown in block 609.

[0041] Similarly FIG. 7 is a flow chart of a method in which theinjection of the calibration signal is not triggered or initiated by thereception of the signal of interest.

[0042]FIG. 7 is an simple flow chart of an embodiment of the presentsubject matter utilizing the above approach to determine the AOA of afrequency hopping signal from a mobile appliance which includescalibrating the signal path between from the antenna array to thewireless location sensor for the frequency hops having the samefrequency using only one calibration signal, calibration coefficient andspecific frequency hops. In the first step the frequency hoppingsequence of the hopping sequence of the signal (f₁,f₂ . . . f_(N)) isobtained as shown in block 701. The calibration source injects a singlecalibration signal at a frequency f_(k) selected from the frequencies ofthe hopping sequence (f₁,f₂ . . . f_(N)) into the path as shown in block703. This calibration signal is used to determine a calibrationcoefficient C_(k) for the frequency f_(k) as illustrated in block 705.The calibration coefficient C_(k) is used only to calibrates thefrequency hops having the frequency f_(k) and is stored for latter useas shown in block 707. The mobile's signal is then received at themulti-element antenna array over multiple hops of frequency f_(k) asshown in block 709. The calibration coefficient C_(k) is used only tocalibrates the frequency hops having the frequency f_(k). The WLScollects energy from only those frequency hops with a frequency f_(k),these hops, along with the calibration coefficient C_(k) are used todetermine the AOA of the received signal as shown in block 711.

[0043] In an additional embodiment of the disclosed subject matter,periodically, and unrelated to the signal of interest collection times,calibration data can be collected on all of the hopping frequencies.This data can be updated and statistically manipulated to create arunning database of the calibration coefficients (C₁ . . . C_(M)) forall of the frequencies (f₁ . . . f_(M)) of the possible frequencyhopping sequences (f₁ . . . f_(N)) where M≧N. Therefore at any time afrequency hopping signal is received there is a previously determinedcalibration coefficient for each frequency in the frequency hoppingsequence.

[0044]FIG. 8 is a simplified illustration of the above embodiment. Thecalibration source injects calibration signals of known frequencies (f₁. . . f_(M)), which represents all the frequencies in the possiblehopping sequences (f₁ . . . f_(N)) into the path as shown in block 801This injection can be periodic or manually initiated. The calibrationsignals are used to determine calibration coefficients (C₁ . . . C_(M))corresponding to the frequencies (f₁ . . . f_(M)) as illustrated inblock 803. These calibration coefficients is also stored in an memorydevice. A signal is subsequently received at the multi-element antennaarray as shown in block 807 and the calibration coefficients stored inthe memory are applied to the received signal to thereby to calibrateeach of the frequencies (f₁ . . . f_(N)) of the received signal to thepath as shown in block 809. The coefficients stored in the database canbe statistically manipulated, to provide averages, weighted averages,mean, median or other statistics such that the particular calibrationcoefficient for a corresponding frequency is a function of more than onecalibration signal at that frequency.

[0045] Another embodiment of the disclosed subject matter, periodically,and unrelated to the signal of interest collection times, collectscalibration data on all of the hopping frequencies as previouslydescribe in relation to FIG. 8. This data can then be used to derive arelationship between the calibration data at each of the hoppingfrequencies. For example, if the hopping frequencies are f₁,f₂,f₃ andf₄, then the phase and amplitude of the calibration coefficientsC₁,C₂,C₃ and C₄ for each of the antenna elements paths for f₂, f₃ and f₄can be referenced to f₁ with a general expression of beingC_(x)=F(C_(z),f_(x),f_(z)). In this example C₂=F(C₁,f₂,f₁) andC₃=F(C₁,f₃,f₁). The calibration coefficients for the several frequenciescan also be determined with a relationship with two or more calibrationcoefficients determined for two or more reference frequencies, whichcould be generally described as C_(x)=F(C_(z),C_(y), . . .C_(N),f_(x),f_(z),f_(y), . . . f_(N)). The premise is that although thecalibration may change over time, the relationship from one frequency toanother remains somewhat constant. Then calibration can be done on asingle RF frequency either just prior or just after the signal ofinterest collection event, and the other calibration data could bederived for the remainder of the frequencies in the hopping set usingthe single RF frequency calibration data and the previously derivedrelationship between the frequencies. The calibration equipment requiredto implement this approach would be similar to that used for the singleRF frequency case.

[0046]FIG. 9 is a simple flowchart illustrating the above method. Thecalibration source injects calibration signals of known frequencies (f₁. . . f_(M)), which represents all the frequencies in the possiblehopping sequences (f₁ . . . f_(N)) into the path as shown in block 901This injection can be periodic, manually initiated or some otherfrequently occurring trigger. The calibration signals are used todetermine calibration coefficients (C₁ . . . C_(M)) corresponding to thefrequencies (f₁ . . . f_(M)) as illustrated in block 903. Thesecalibration coefficients are used to determine relationships relatingcalibration coefficient of one frequency to the calibration coefficientsof each of the other frequencies using the stored calibrationcoefficients, such as the relationship C_(i)=F(C_(j),f_(i),f_(j)) wherej=1 to N identifies the reference frequency and i=1 to N identifies thefrequency who coefficient is to be determined as shown in block 905. Theone frequency to be used as a reference frequency can be arbitrarilyselected or can be selected as a function of a statistic of all thefrequencies in the hopping sequence, such as an average, mean, mode,first moment or other statistic of the frequencies in the hoppingsequence.

[0047] The relationships exemplified by the functions are also stored inan memory device. The WLS obtains the frequency hopping sequence of thesignal (f₁ . . . f_(N)) as shown in block 907 and then receives thefrequency hopping signal from the mobile appliance as shown in block909. After receiving the signal which is a triggering event, thecalibration source injects a single calibration signal at a referencefrequency f_(k) as indicated in block 911 and uses the calibrationsignal to determine the calibration coefficient C_(k) a the referencefrequency f_(k) shown in block 913. The method then uses the determinedrelationships or ratios to derive the calibration coefficients (C₁ . . .C_(N)) for each of the remaining frequencies in the frequency hoppingsequence (f₁ . . . f_(N)), such that C_(i)=F(C_(j),f_(i),f_(j)), thus(C₁ . . . C_(N)) becomes (F(C_(k),f₁,f_(k)), . . .F(C_(k),f_(N),f_(k))). The calibration coefficients determined from therelationship are then applied to the received signal to thereby tocalibrate each of the frequencies (f₁ . . . f_(N)) of the receivedsignal to the path as shown in block 917.

[0048] While preferred embodiments of the present inventive system andmethod have been described, it is to be understood that the embodimentsdescribed are illustrative only and that the scope of the embodiments ofthe present inventive system and method is to be defined solely by theappended claims when accorded a full range of equivalence, manyvariations and modifications naturally occurring to those of skill inthe art from a perusal hereof.

What we claim is:
 1. A method of calibrating an antenna array and signalprocessing system for receiving a frequency hopping communication signalcomprising the steps of: obtaining a frequency hopping sequence of thecommunication signal; receiving the communication signal; injecting acalibration signal at one frequency of the frequency hopping sequence ofthe communication signal in response to receipt of said communicationsignal; determining a calibration coefficient C₁ for said one frequency;and, applying C₁ to a received signal at each frequency of the receivedsignal.
 2. The method of claim 1 wherein the received signal is saidcommunication signal.
 3. The method of claim 1 wherein the receivedsignal is a later received signal.
 4. The method of claim 1 furthercomprising the step of determining the AOA of the communication signalbased on said communication signal and C₁.
 5. The method of claim 1wherein said frequency hopping sequence is comprised of N frequenciesf_(i) where i=1 to N and the calibration coefficient C₁ is associatedwith each f_(i).
 6. The method of claim 1 wherein the step of injectingthe calibration signal is proximate in time to receiving the receivedsignal.
 7. The method of claim 1 wherein the one frequency is determinedas a function of an average frequency of the hopping sequence.
 8. Themethod of claim 1 wherein the one frequency is the first frequency inthe frequency hopping sequence.
 9. The method of claim 1 wherein the onefrequency is arbitrarily chosen from the frequency hopping sequence. 10.The method of claim 1 wherein the one frequency is determined as afunction of a first moment of the frequencies in the frequency hoppingsequence.
 11. A method of calibrating an antenna array and signalprocessing system for receiving a frequency hopping communication signalcomprising the steps of: obtaining a frequency hopping sequence of thecommunication signal injecting a calibration signal at one frequency ofthe frequency hopping sequence of the communication signal in responseto receipt of said communication signal; determining a calibrationcoefficient C₁ for said one frequency; storing said calibrationcoefficient C₁, receiving the communication signal; and, applying thecalibration coefficient C₁ to the communication signal for eachfrequency of the communication signal.
 12. The method of claim 11wherein the step of injecting a calibration signal is initiatedperiodically.
 13. The method of claim 11 wherein the step of injectingis triggered in anticipation of receiving said communication signal. 14.The method of claim 11 further comprising the step of determining theAOA of the communication signal based on said communication signal andC₁.
 15. The method of claim 11 wherein said frequency hopping sequenceis comprised of N frequencies f_(i) where i=1 to N and the calibrationcoefficient C₁ is associated with each f_(i).
 16. The method of claim 11wherein the one frequency is determined as a function of an averagefrequency of the hopping sequence.
 17. The method of claim 11 whereinthe one frequency is the first frequency in the frequency hoppingsequence.
 18. The method of claim 11 wherein the one frequency isarbitrarily chosen from the frequency hopping sequence.
 19. The methodof claim 11 wherein the one frequency is determined as a function of afirst moment of the frequencies in the frequency hopping sequence. 20.In a network overlay geolocation system, a method for locating a mobileappliance including determining the AOA of an uplink signal from themobile appliance at a base station from measurements, by a wirelesslocation sensor, of an attribute of the uplink signal and a frequencyspecific calibration of a path between a multi element antenna array andthe wireless location sensor, the improvement comprising the steps of:(a) collecting segments of a frequency hopping signal associated with aspecific hop; (b) calibrating the path, at approximately the specifichop's frequency, proximate in time to the collecting of the segment,over a plurality of hopping sequence cycles; and, (c) estimating the AOAof a frequency hopping signal from the collected segments associatedwith the specific hop and the path calibrations at approximately thespecific hop's frequency.
 21. The method according to claim 20 whereinthe step of calibrating includes generating a calibration signal. 22.The method according to claim 20 wherein the step of calibratingincludes tuning the calibration source to the specific hop frequency.23. The method according to claim 20 where the plurality of hoppingsequence cycles is based on hop duration.
 24. The method according toclaim 20 wherein the network is a GSM system.